This invention relates to an improved system for interfacing an encoder with phase quadrature outputs, such as a displacement sensor, to a microcomputer.
It is necessary to supply a computer with accurate displacement data which is used by a real time multivariable adaptive algorithm to control the formation of a resistance spot weld in process. A description of the microprocessor-based adaptive controller is given in the inventor's concurrently filed application Ser. No. 386,153, which is assigned to the same assignee. The overhead of the interface should be reduced to a theoretical minimum. Currently available peripheral interfaces that measure displacement information require significant processor overhead to acquire the data and to put it in a form which is recognized by the computer language. This discreases the amount of available computer time remaining for the implementation of an adaptive control algorithm, thereby reducing the complexity of the algorithm which can be programmed. A specific object of this invention is to provide a more efficient digital displacement interface which does not have to be managed by the processor.
The prior art method of interfacing the displacement device in the drawings to a computer in a format recognizable by most languages is as follows. The computer (1) asserts a data request signal through an output port; (2) waits for an asynchronous signal to signify that the displacement unit is finished processing the last displacement data point from the input transducer; (3) outputs a binary address corresponding to the decimal digit to be read; (4) reads the value of the digit through an input port; (5) repeats steps (3) and (4) for each decimal digit on the display; (6) reads the sign (+ or -) through an output port (7) performs a BCD (binary coded decimal) to binary conversion on the input data; and (8) stores the result in a set of memory locations assigned to the displacement variable by the computer language. This process is repeated each time the displacement value is updated. The procedure is very cumbersome, requiring much computer overhead.